The present invention is directed to a radiation mask having a masking structure and a carrier therefor, designed to produce desired structural configurations in photosensitive resists by the utilization of x-ray radiation, aligning or registration marks being provided on the carrier.
From the publication "Solid State Technology", July 1972, pages 21 to 25, there is disclosed, that for manufacturing semiconductor devices with structural dimensions in the micron range, x-rays can be used to expose the photosensitive resist. The use of x-rays for the exposure enables more accurate reproduction of the masking structures on the photosensitive resist layer because of the reduction in diffraction phenomena, in particular if a space must be maintained between radiation mask and photosensitive resist layer during the exposure. According to the prior art, the x-rays are also used in the alignment of the geometric position i.e. registration alignment of the radiation mask with respect to the semiconductor wafers upon which the photosensitive resist layer is disposed.
The use of x-rays for the alignment of the positions of the semiconductor wafers involves a relatively large outlay in terms of x-ray equipment. Furthermore, additional operations have to be performed on the semiconductor wafers as the latter must be etched thin at corresponding locations. Moreover, when working with x-rays, considerable safety precautions must be taken to protect the operators, so that again an additional outlay is required.
The present invention, therefore, has among its objects to make possible, in the context of lithographic processes in which structural configurations are to be produced in the photosensitive resist by x-ray radiation, to avoid the necessity of utilizing x-rays for the period of time involved in effecting alignment operations in connection with the registration of the semiconductor wafers with the radiation mask.
This object is achieved in accordance with the invention by the utilization of a radiation mask of the type heretofore described in which the carrier comprises a layer of material, of approximately 3 to 10 .mu.m in thickness, which material is penetrable by x-rays and by radiation in the visible part of the spectrum.
The invention proceeds from the recognition that when observing aligning marks with the microscope the semiconductor wafer carrying the photosensitive resist must not be traversed by radiation. For alignment purposes, a microscope utilizing light from the visible part of the spectrum can be utilized if the carrier of the radiation mask also is penetrable by such radiation.